Re: Stereo base calculator

[bercov@xxxxxxxxxxx (John Bercovitz)]

> Let me know what you think!

OK  8-)

I gave it a try:

  Stereo Base Calculation

  Input Parameters

  Lens focal length 50 mm

  On-film deviation 1.2 mm

  Near point 200 mm

  Far point 220 m.

  Calculated Result

  Stereo base  52.8 mm

This looks very good to me!  The geometrically correct answer is
40.2 mm but I'm not sure it's worth the extra complication of MAOFD 
to get it.  I guess you could add a caveat about close distances.
The approximation you used:

          D * S2 * S1
    B = ---------------
         F * (S2 - S1)

  where:

    B  = Base separation
    D  = Deviation on film
    F  = focal length of lens
    S  = best focus distance for range of S1->S2 [added for MAOFD, below]
    S1 = distance to near object in picture
    S2 = distance to far object in picture.

The geometrically exact [MAOFD] formula:

         D * S2 * S1
    B = ------------- * [1/F - 1/S]
           S2 - S1

  where:
         2 * S2 * S1
    S = -------------
           S2 + S1

As you can see, the only difference is the addition of 1/S and that
only becomes important as S approaches F.  Besides, by the time you
get into entrance pupil calculations, even MAOFD gets slightly off
since it is based on the entrance pupil being at the primary nodal
point, which is very close to true in most lenses, but not highly
asymmetrical lenses so you'd need a caveat for asymmetrical lenses.
8-)

You might say on the front page that you are using D = 1.2, 2.5 mm

John B